(1) Field of the Invention
The present invention relates to a control method and a control unit for controlling a manipulator, more particularly a control method and a control unit for controlling the operation of the manipulator, capable of performing a high speed positioning control of the manipulator with a high accuracy.
(2) Description of the Prior Art
Recently, differnet control units for industrial robots, i.e. manipulators, having functions resembling the upper limbs of a human body, have been proposed in which microprocessors are widely used as control means.
FIG. 1 shows an example of a block diagram of the control unit for a manipulator according to the prior art. In the figure, a model following-up type control unit 51, which is constructed by a microprocessor, performs the positioning control of a manipulator 53 as an control object in such a manner that actual joint angle .theta. of the manipulator 53 can follow along a target joint angle .theta..sub.r. The control unit of this kind comprises a reference model 55, an integrator gain means 59, 61, and 63 and adders 65 and 67.
The control unit 51 controls the joint angle .theta. of the manipulator 53, so as to determine a control input signal u to the manipulator 53 by the following equation, in accordance with the joint angle .theta., joint angle speed .theta., reference model joint angle .theta..sub.M, and reference model joint angle speed .theta..sub.M ; ##EQU1## where F.sub.1, F.sub.2, F.sub.3 indicate each control gain of the gain means 59, 61, 63, respectively and e indicates an output of the adder 65, which is e=.theta.-.theta..sub.M.
The reference model 55 in the control unit 51 for each arm shaft of the manipulator 53 according to the prior art can arbitrarily be constructed as a model of the secondary transfer function as expressed by the following equation. ##EQU2##
Namely, the reference model 55 produces the reference model joint angle .theta..sub.M and the reference model joint angle speed .theta..sub.M corresponding to the target joint angle .theta..sub.r by defining the parameters a.sub.1, a.sub.2, and K in the transfer function T.sub.(s) of the model expressed by equation (2).
In the control unit 51 for the manipulator according to the prior art, the approach for defining the parameters of the reference model 55 is fixed. As a result, when a stepping width or moving angle .theta..sub.W of the manipulator 53 from the starting point to the end point of each arm shaft of the manipulator 53 differs from shaft to shaft, in other words, when the target joint angle .theta..sub.r of each shaft of the arms of the manipulator differs from each other, the so-called positioning time T.sub.r correspondingly differs. Namely, a necessary time for settling the deviation of the actual joint angle .theta. to the target joint angle .theta..sub.r within a predetermined allowance or angle tolerance .+-..DELTA..theta. with respect to each arm shaft of the manipulator differs from each other as shown in FIG. 2, although the dynamic characteristics of the reference model 55 are equal and this results in the difference among the positioning times of each arm shaft. As a result, the positioning time of each arm shaft can no longer be uniform, with the result that the movement of the arms of the manipulator 53 becomes irregular. Hence, a high speed positioning control of the shafts in the prior art due to so-called PTP operation became difficult.